Portable disc sanders and the like include an electric motor in a housing with handles for holding same and a motor shaft extending from the housing for removable engagement with a sanding disc. The sanding disc itself may be formed as a cloth or paper element having an abrasive material on the front face thereof and normally a disc of this type is mounted upon a backing plate or backing disc and secured to the shaft end. A wide variety of different types of backing discs have been developed and employed. An early and favorite type of backing disc is formed of rubber and improvements thereon include thin metal discs and various types of plastic and Fiberglas discs.
The backing disc for a rotary disc sander provides the requisite rigidity to the abrasive sheet so that the latter may be forced against the workpiece as it is rotated and yet the backing disc should have at least limited flexibility. An early attempt at controlling the flexibility of a backing disc is shown in U.S. Pat. No. 1,778,470 wherein outwardly tapering ribs of varying configuration are employed in the back of the disc. Other improvements in backing discs have related to structures for automatic or self-cleaning of the abrasive surface, as illustrated, for example, in U.S. Pat. Nos. 3,110,140 and 3,187,475.
It is commonly accepted that portable power driven sanders and the like discharge sanded particles and dust rather indiscriminately into the atmosphere. It is recognized that this pollution of the atmosphere is harmful to operators and those in the vicinity as well as being undesirable from the viewpoint of depositing a film of dust upon surrounding surfaces. An operator may be at least partially protected by a mask; however, it is normally not feasible to cover all surrounding surfaces. Certain attempts have been made with stationary grinders, sanders and the like, to exhaust the particles ground or sanded from workpieces by the provision of separate or integral exhaust systems operating in the housing of the apparatus. Stationary equipment of this type is normally employed by manipulation of the workpiece so that exhaust systems are practicable; however, portable sanders or the like are operated by manipulation of the sander so that the operator must have a full view of at least the backing disc and thus housings thereabout for exhausting particles are not practical.
The present invention provides an improved backing disc for portable rotary sanders or the like providing for the ejection of particles, dust and the like, in a predetermined direction from the rotary equipment so that this material may be directed away from an operator and other surfaces in the area to be protected and may, in fact, be collected for disposal.